High-power and narrow-linewidth laser sources can benefit a wide range of applications. For example, high-power and narrow-linewidth lasers operating at about 1.5 μm to about 1.6 μm and second harmonic generation (SHG) at around 780 nm can be useful in quantum optics experiments, such as pumping an optical parametric oscillator (OPO) to generate a non-classical state at telecommunication wavelengths. In another example, 780 nm is the transition wavelength of the D2 line of Rubidium (Rb) atoms, and lasers at this wavelength can be used in atomic physics, such as laser cooling and internal state preparation of Rb atoms. In yet another example, high-power and narrow-linewidth lasers can be used in chemical sensing, such as Raman spectroscopy, to detect trace amounts of toxic substances or explosives.
A conventional technique to control the linewidth of lasers uses an active feedback system to monitor the output beams of the lasers and control the operation of the lasers to achieve the desired linewidth. Active feedback systems typically include complex electronics and detectors, which can be expensive. In applications for chemical sensing, the active feedback system can also increase the size, weight, and power (SWaP) of the resulting sensor, thereby limiting the portability and compactness of the sensor.